How the SpillNot works:

When you hold a cup of juice while walking, the juice tends to spill because the cup accelerates forward (ax, FIG.1, green arrow) and backward (-ax) with each step. The juice tips in response to that acceleration, and may spill over the rim of the cup. The Spill Not automatically tips the cup so that its top stays parallel to the juice surface (FIG.2). For example, if the juice surface tips to 30 deg, but the cup stays horizontal, the juice could spill. But if the cup also tips to 30 deg, we get no spill! Note that there are only 2 forces on each portion m of juice…the weight mg down, and the buoyancy force Fb of the juice pushing at a right angle to the surface. These two forces result in a horizontal accelerating force ma (in red). We see from FIG.1 that

Bubbles in tubes offer many advantages over spheres on ramps for velocity and acceleration experiments:

The bubble stays in the tube! There are no escaped marbles to chase down.

The bubble moves more slowly than a marble, permitting more accurate determination of elapsed time.

Results are highly reproducible.

Many data points can be collected in a short period of time.

A Speed of the Bubble Apparatus to hold and protect the tube is easy to construct from scrap and/or inexpensive materials. It enables even very young students to obtain highly reproducible data quickly. It also protects the tubes from being damaged if dropped or bumped. Plans and suggested materials are included in this blog. The following experiment is one I use with the elementary students in our after school science club. Read the rest of this entry »

Newton was a revolutionary thinker of his time. He is responsible for the three laws of motion that we still use today;

1. Objects that are not in motion remain stationary unless acted upon by another force.

2. There is a direct relationship between the force acted upon the object and the mass of that object times the acceleration the object feels (F=ma).

3. For every action there is an equal and opposite reaction.

Nobody before Newton could explain why objects acted the way they did, but with these three laws he quantified movement in terms everyone could understand.

But there was a problem with his theory; if all motion had to be caused by some force acting on it, then why do objects fall towards the earth when you release them from a fixed position? This free falling object was in fact free, meaning free of outside forces acting upon it (besides wind resistance). There were no visible forces acting upon that object. So why do they move downward if nothing is acting on it? But Newton explained this motion with gravity. He said that gravity is a force that the earth has upon all objects, something invisible that pulls us down at all times at a constant acceleration. There is a myth that the way Newton thought of the idea of gravity was when he was thinking about it under an apple tree when an apple fell on Newton’s head and at that moment, he figured out that there must be a force pulling the object down. This is also why apples are used to demonstrate Newton’s force, but no one knows definitively if the myth is true or not. Read the rest of this entry »